Bump tensorflow in /model_tools/tools/tensorflow2caffe

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.15.4 to 2.12.1.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v1.15.4...v2.12.1)

---
updated-dependencies:
- dependency-name: tensorflow
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

model_tools/tools/tensorflow2caffe/requirements.txt

@@ -1,2 +1,2 @@
 numpy==1.18.1
-tensorflow==1.15.4
+tensorflow==2.12.1